A government agent that provides electronic data for libraries and information centers wants to find out customers need what kind of new data.Then the information expert from this government agent is invited to join in a meeting held by a shopping center in the public place. Besides, customers of other eight agencies will also attend the meeting. The well-trained host investigates information used by attendees and intends to know their new demands. The one-way mirror is used in the meeting process to observe its discussion status. After the meeting, the company who hires the host will provide minutes to the government, what is the market research method involved in the above situation? 一家为图书馆和信息中心提供电子数据的政府机构发现客户需要哪些新数据，来自政府机构的信息专家应邀参加在一家购物中心的办公场所举办的会议，另有其他八家机构的客户也出席参加，会议由训练有素的主持人调查了与会者目前使用什么信息以及想知道什么新信息， 会议过程中通过单面镜观察会议的讨论情况，会议结束后，雇佣主持人的公司向政府提供会议记录，这是采用了哪种市场调研方法？